Led by Durham University in the UK, a team of international researchers conducted a global analysis of plants and animals to determine the prevalence of established alien species. The study results were published in the journal Nature Ecology & Evolution.
During the study, scientists combed through existing data for 423 mainland regions and 186 island regions, looking at eight different groups including ants, amphibians, freshwater fish, birds, spiders, reptiles, mammals, and vascular plants. The data revealed established hotspots for alien species.
Dr. Wayne Dawson, with the Department of Biosciences at Durham University and the lead author of the study, said these species were found mostly to inhabit coastal mainland and island regions. He contributes these findings to the fact that these areas all have major points of entry, such as ports. Areas that had the highest concentration of established alien species were the Hawaiian Islands, the Lesser Sunda Islands in Indonesia, and the North Island of New Zealand.
The Hawaiian Islands had the highest number of established alien species across all of the eight study groups, including feral hogs in the mammal group and guppies in the fish group. New Zealand had the second highest number with predatory mammal species such as cats, possums, and rats, which present a real problem for the country’s native bird species. In addition, approximately half of New Zealand’s plant life is made up of established alien species.
Other areas of concern include the United Kingdom, with an emphasis on England and the U.S. state of Florida. England in particular has more established alien species, both plants and animals, than many other regions around the globe. Some of these species include the rose-ringed parakeet, grey squirrel, the false widow spider, and the Himalayan balsam plant. Florida is the top hotspot among all the coastal mainland regions with alien species such as the Burmese python and a large number of ant species.
Study results revealed certain factors that affect alien species, such as the wealth of a region, the density of human population, and the region’s climate. While these factors vary from region to region and species to species, areas that are wealthier and have fewer human inhabitants, such as island regions, have more alien species.
Dawson said more research is needed in order to determine whether these effects occur because a higher number of species are introduced to these regions, or because disturbances by humans make it easier for the alien species to find areas in which they can live and thrive. Many of these alien species are useful and they will not spread; however, Dawson said some species will spread, and the impact to native species and ecosystems will vary.
The challenges researchers face are to understand the various impacts alien species have on a region and to determine how to deal with the changes they cause. They must also determine how to prevent more alien species from being introduced to the world’s regions that are the most vulnerable.
Dawson said more effective measures would include heightening biosecurity protocols such as those currently in place in New Zealand to detect alien species and prevent them from entering the country. In addition, Dawson said when a species is proposed for introduction to a region, careful vetting measures such as those carried out by the European and Mediterranean Plant Protection Organization (EPPO) is needed to exclude species from being allowed to enter a region where they would have the potential to establish and have a negative impact.
By Trixie Dillwood
Photo Courtesy Pablo Garcia-Diaz